Optimization　of　the　modified　University　of　Cape　Town　(UCT)　step　feed　process　at　low　temperatures　was　investigated　to　improve　the　nitrogen　and　phosphorus　removal　capacities.　Nearly　complete　nitrification,　desired　denitrification　and　phosphorus　uptake　could　be　obtained　at　temperatures　ranging　from　19.2°C　and　27.3°C　with　the　hydraulic　retention　time　(HRT)　of　8h.　However,　a　drop　in　temperature　to　18.5°C　and　then　to　16.5°C　led　to　the　nitrification　deterioration　in　spite　of　the　increase　of　HRT　to　be　9h,　but　it　gradually　recovered　to　the　normal　level　with　HRT　of　10h.　Moreover,　there　were　more　nitrates　accumulated　in　the　effluents　owing　to　lower　denitrification　rates,　which　decreased　from　42.5　mgN/(gVSS·d)　in　phase　1　to　28.6　mgN/(gVSS·d)　in　phase　3.　However,　the　PO43--P　removal　capacities　were　not　seriously　influenced　by　the　drop　of　temperatures,　just　with　a　little　decrease　of　removal　efficiency.　Because　the　reduced　nitrification　temperatures　led　to　change　the　anoxic　zone　into　another　additional　anaerobic　zone,　which　was　beneficial　to　the　enrichment　of　anaerobic　microbial　populations.　In　addition,　good　settling　property　with　the　mean　SVI　of　88.9　mL/g　might　be　associated　with　the　step　feed　strategy　and　the　existence　of　anaerobic　zone　in　the　process　configuration.　©　2011　IEEE.